The present invention relates to a control system for controlling a hand of an industrial robot.
Many industrial robots have heretofore been developed for use in materials handling or spot welding and adapted to be driven under PTP control (i.e. point-to-point control). Recently, the robots tend to be increasingly used in various industrial fields for arc welding, assembling and others, and the PTP control tends to be replaced by a CP control (i.e. continuous path control) which assures higher performance.
The CP control involves a method of storing in a memory device data obtained at every sampling time of the control circuit incorporated in the robot. This method however requires an enormous storage capacity because a great deal of data must be stored for the particular arc welding, assembling or other operations to be performed. Such being the circumstances, the teaching is usually effected under the PTP control and a continuous path is generated through linear interpolation of spans between the points given by the teaching for driving the robot.
In this connection, it is noted that in case the hand of the robot is caused to move at a certain speed along the path defined by two line segments so as to pass the points determined through the linear interpolation, acceleration would become infinite at a nodal point of the path, making the control impossible, unless the path is so modified in the vicinity of the nodal point that one line segment passes over to the other succeeding line segment continuously along a curved path. To this end, there have been proposed methods of interconnecting the two polygonal line segments by an arc or a curve of multi-degree. However, these prior art methods are disadvantageous in that difficulty is encountered in arithmetically determining the path on a real time base upon driving the robot because the amount of calculations for determining the path will be significantly increased and that the teaching becomes extremely complicated. For these reasons, it is difficult to adopt the prior art methods mentioned above for practical applications.
The robot's hand thus has to be stopped at the taught point, providing a major cause for elongating the time required for the operation of the robot.
Further, for controlling the attitude of the robot's hand by resorting to interpolation, a rotation angle or deviation in contraposition of the robot mechanism is divided equally. However, since the rotation angle mentioned above is inherently in a non-linear relation with the attitude, there will be a remarkable difference in data for different types of robots. This is disadvantageous because when the robot is to be driven under a direct numerical control (DNC) or the like, data can not be used in common for different types of robots, while linear interpolation which allows a uniform rotation speed is difficult and, therefore, also disadvantageous.
Further, there is known a method of controlling the attitude of the robot's hand through interpolation by making use of a Eulerian angle. However, representation by Eulerian angle includes a singular point, as the result of a which an attitude which can not be represented in terms of a Eulerian angle is inevitably present. Besides, the linear interpolation which makes the rotation speed uniform is difficult, as is the case of the control performed on the basis of the rotation angle described above.
With a view to solving the problems arising in conjunction with the control of the robot's hand described above, the present invention provides a method of interpolating the path by continuously interconnecting a plurality of straight line segments with parabola by resorting only to the arithmetic interpolating functions inherently incorporated in the conventional robot. Since the inventive method can be carried out solely by the operation of the linear interpolation, the addition of a long program is not necessary, whereby the amount of calculations may remain small, providing the operation of a real time base to drive the robot. As to the attitude interpolation of the robot's hand, there is proposed according to the invention a method of driving the robot through interpolation of the rotation angle with the attitude being represented by two unit vectors. According to the inventive method, interpolation of the attitude of the robot's hand can be accomplished with an improved accuracy.
Accordingly, it is an object of the present invention to provide a control system for a robot's hand which is capable of determining the path for the movement of a robot's hand through interpolation based on simplified arithmetic processing on a real time base.
It is another object of the present invention to provide a robot hand controlling system which is capable of varying the speed of the hand at a uniform acceleration through simplified arithmetic processing.
According to a general aspect of the present invention, arithmetic interpolation processing is employed to divide spans among individual positions set for determining a path along which the robot's hand is to be moved, whereby the path for the robot's hand originally defined by a polygon or line segments is made continuous by a parabola in the vicinity of a nodal point so that the hand moves at a uniform acceleration in the vicinity of the nodal point.
According to another general feature of the invention, the attitude of the hand is represented by two unit vectors f and g, wherein a rotation axis for motion of the robot's hand on the basis of two sets of given data (f.sub.o, g.sub.o) and (f.sub.n, g.sub.n) representative of attitudes of the hand, respectively, and the rotation angle required for the robot's hand to move from the one attitude given by (f.sub.o, g.sub.o) to the other (f.sub.n, g.sub.n) about the rotation axis defined by (f.sub.o -f.sub.n).times.(g.sub.o -g.sub.n) is interpolated for driving the robot's hand.
The above and other objects, features and advantages of the present invention will become more apparent by reading the following description of the preferred embodiments of the invention made with reference to the accompanying drawings.